(a) Field of Disclosure
The present description relates generally to a thin film transistor array panel such as used in flat panel displays and to a mass production manufacturing method of a thin film transistor array panel. More particularly, the present description relates to a thin film transistor array panel and a manufacturing method of a thin film transistor array panel to reduce breakage of data line metal due to corrosion caused by receiving a corrosive attack because of stripping away of an organic layer and an insulating layer to thereby expose a data contact pad. Also, the disclosure relates to formation of the data contact pad so that it can be easily contacted with.
(b) Description of Related Technology
A liquid crystal display (LCD) is one type of flat panel display that is now widely used. The typical liquid crystal display includes two display panels in which field generating electrodes such as pixel electrodes and a common electrode are formed, and a liquid crystal layer is interposed between the display panels. The pixel-electrodes are often formed of a transparent conductive material such as ITO. A voltage is applied to the field generating electrodes to thereby generate an electric field extending into or through the liquid crystal layer, which field then determines the direction of liquid crystal molecules of the liquid crystal layer, and an image is displayed by controlling the polarization of incident light or of backlight provided light.
The two display panels of the liquid crystal display include a thin film transistor (TFT) array panel formed with various signal lines, thin film transistors, and pixel electrodes, and a common electrode panel formed with a common electrode.
The thin film transistor (TFT) array panel includes signal lines such as gate wires and data wires, and also has transparent pixel electrodes formed thereon (e.g., made of ITO). The signal lines extend to edge connection pads where the latter are disposed in peripheral non-display areas of the TFT array panel and where the edge connection pads are used for connection with external circuitry such as with gate line driver ICs and data line driver ICs. An insulating layer is formed between the signal lines and pixel electrode regions for defining sufficient insulation therebetween.
The insulating layer is generally made of a silicon nitride (SiNx), and is deposited on the signal lines through chemical vapor deposition (CVD). If the signal lines are disposed too close to the pixel electrodes, excessive crosstalk may be generated, and this crosstalk may be due to the silicon nitride between the signal lines and the pixel electrodes being too thin and thus tending to function as a signal coupling dielectric material such that an excessively large capacitance is formed therebetween.
To reduce or prevent the crosstalk, the thickness of the silicon nitride (the distance between the signal line and the pixel electrode) is often supplemented substantially to thereby decrease the capacitance. However it is not easy to thicken the insulation by depositing more the silicon nitride with a desired thickness through chemical vapor deposition because it takes a long time. Accordingly, to solve this problem, a method in which an organic layer is thickly coated on the signal lines through a coating method has been proposed.
When the gate wire, the gate insulating layer, an active layer, the data wire, and a data insulating layer are formed, and the organic layer is formed on the data insulating layer in the thin film transistor array panel. If the thickness of the organic layer at the contact pad portions of the TFT panel is relatively large; and thus the contact pads are recessed deep under the top of the organic layer due to increased thickness of the organic layer, then conductive balls or other like means that are used for resiliently contacting with the pad and thereby connecting it with external circuits such as ICs are pushed up relative to the recessed contact pads such that increased contact resistance may occur between the external circuit and the pad, and as a result, a signal transfer deterioration may develop. In one embodiment, the conductive contact-making balls are provided on a flexible thin film ribbon connector which is used during manufacture to connect the TFT array panel with external circuitry. Particularly, when the external circuitry uses multiple channel ICs such as with 960 data lines present in the panel, the pitch between the contact pads may be as small as 37 μm such that the width of the SD pad metal (side of display contact metal) is only 20 μm after etching, and if the width of the exposure opening through the organic layer is less than the width of the opening in the SD pad portion, given possibility of a misalignment overlay, then the contact openings through the organic layer at the contact pad locations may be only about 11 μm each, and thereby the above-described deterioration of contact may be often present.
Accordingly, to prevent or reduce this, a means should be devised where the effective thickness of the organic layer in the pad contact portion of the panel is less than the thickness of the organic layer in the display area of the panel.
One exemplary method disclosed herein for reducing the effective thickness of the organic layer in the pad contact portion of the panel relies on forming the organic layer from a composition that defines a negative photosensitive film (Nega-PR). Then a photolithography mask is defined with etch control gratings so that some portions of the Nega-PR receive a greater amount of light and are thus correspondingly not etched away while other portions that do not receive much light are correspondingly etched away to a greater degree. In one embodiment, the photomask for the Nega-PR organic layer has wave-like ripples or slit patterns formed therein in the areas corresponding to the pad contact portions of the panel where the slits are formed with a Cr metal pattern and each on-photomask slit piece has a line width of less than the resolution of a light exposer such that patterning light is transmitted through the photomask and to the Nega-PR organic layer with varying degrees of intensity and thus the resulting post-etch height of the organic layer can be selectively controlled so as the proved reduced effective thickness in the region of the contact pads.
In conventional art, the photomask slits extend perpendicularly relative to the data lines extending from the contact pads and the organic layer is a Positive-PR type. The reason for this is to avoid misalignment problems. If instead, the direction of the slits had been formed parallel to the direction of the data wires, then if the substrate and the mask for the organic layer are mis-aligned, problems will ensue at the end of the data wire that is to be exposed for defining a contact area (by etching away of the organic layer at that spot) and which should thus have a corresponding opening in the Cr metal directly over it for causing substantial etching under the normal condition of using the positive photosensitive organic layer (Posi-PR). However if there is misalignment that pad contact area will instead lie partly under a dark portion of the Cr metal such that the post-etch thickness of the organic layer is increased by the lowered exposure amount. As a result, the to-be-exposed end section of the data wire may not be properly exposed. Elsewhere, the misalignment will cause too little of a thickness of the organic layer to remain and this will reduce protection against attack by corrosive chemicals and against consequential deterioration of data line integrity.
After patterning the organic layer by using the mask including the slits with the direction being conventionally perpendicular to the data wires, the data insulating layer is etched by using the patterned organic layer as an etch mask to form wells or depressions at portions of the panel where pixel electrodes will be formed and also at portions of the panel where the pad contacts will be formed.
As described above, the contact resistance between the external circuits and the pad contact portions may be disadvantageously increased due to misalignment caused increase in the thickness of the organic layer such that the signal transmitting deterioration may be generated, and conversely, when the organic layer is thin in other places, the data wires may undesirably receive more attack by corrosive chemicals and thereby disconnection due to wire corrosion may be generated. It is to be understood that some of the above description may not be part of the prior art and thus it should not be treated as an admission regarding what is prior art.